Page 21 - BIOME 2022 | Issue 1

Evolution of flight is another great transition
Image credit: Denise Chan
Figure 6. Archaeopteryx lithographica from
Germany is an ideal transitional fossil be-
tween non-avian dinosaurs and birds.
name. Dinosaurs were either herbivorous
or carnivorous and egg layers and some of
them even had their bodies covered with
feathers like birds. Some of these smaller
dinosaurs with feathers initially began to
glide short distances either to chase prey
or to evade predators. This is believed to
be the birth of birds and transitional fossils turtles, lizards and snakes. This distinct group
dated to be 150–120 million years old having
both dinosaur and bird like characters have
been found (e.g. Archaeopteryx) (Figure 6).
Figure 7. Hypothesized evolutionary relationships of apes based on DNA. The lin-
eages that gave rise to humans and chimpanzees separated about 8 million years
ago.
of life. Because birds evolved from dinosaurs,
birds are also called avian dinosaurs while
the typical dinosaurs are called non-avian
dinosaurs. The reign of the dinosaurs on
earth lasted for nearly 250 million years, and
at the end of the Cretaceous period (145-66
mya) all of the non-avian dinosaurs became
extinct most likely due to an asteroid impact
that caused volcanic eruptions (Cretaceous-
Paleogene extinction event). However, some
of the avian dinosaurs (i.e. birds), crocodiles,
lizards, snakes and amphibians survived this
extinction event and today lizards (7000),
snakes (3900) and birds (11000) are the most
diverse groups of vertebrates in the world.
There was another lineage of vertebrates that
survived the Cretaceous-Paleogene extinction
event. Their origins date back to a group
of reptiles of the late Carboniferous period
which had a skull different from other reptiles
that gave rise to dinosaurs, birds, crocodiles,
of reptiles gave rise to mammals in the
Triassic Period, which include animals that we
are very familiar with including us. Mammals
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